Electron multiplier



April 5, 1941. H. SCHNITGER 2,238,607

ELECTR ON MULTIPLIER Filed Jan. 24, 1959 ATTORNEY Patented Apr. '15,i941 UNITED STATES: PATENT OFFICE Herbert Schnitger, Berlin-Spandau,Germany, assignor to Fides Gesellschaft fiir die Verwaltun: undVerwertung von gewerblichen Schutzrechten mit beschrankter HaftungBerlin, Germany, acorporation of Germany Application January 24, 1939,Serial No. 252,553

In Germany June 8, 1938 1 Claim. (01. 250-175) The invention relates toamplifying tubes and especially the type of tube known as an electronmultiplier.

An object of the invention is to increase the efficiency of the type oftube known as electron I Fig. 1 is a cross-section through a tube havinga preferred embodiment of the invention.

Fig. 2 is an enlarged detailed view of a portion of'Fig. 1.

Fig. 3 is an enlarged detailed view of a modification of electrodestructures of Fig. 2.

Fig. 4 is a cross-section through a modification of the electrodearrangement disclosed in the other figures.

In amplifier tubes, and especially those operated for electronmultiplication through secondary emission, a succession of grid-shapedelectrodes in series is utilized. These grids are connected topotentials which increase as the anode is approached. The amplifyingaction is brought about by the fact that the secondary electronsliberated by the impact of electrons against an electrode come partly bytheir own velocity under the influence of the field of the followingelectrode which field reaches through the grid mesh and these electronsare accelerated and finally strike against the following electrode. Onlya relatively small part of the emitted secondary electrons are under theinfluence of the next following electrode and can attain the next highervoltage. Accordingly, the efficiency of such a tube is small and arelatively high number of steps must be used and also a high voltageapplied in order to obtain the desired degrees of amplification.

The invention contemplates utilizing a magnetic field to increase theproduction of secondaryelectrons in a secondary emission multiplier withscreen or grid-shaped electrodes. This magnetic field lies aboutperpendicular to the discharge path preferably in the direction of thegrid laterals which are so adjusted and dimensioned that under theirinfluence the electrons for the most part strike a part of the surfaceof each individual electrode which is facing the following electrode.Provision can also be made that the mean electron orbit is practicallytangent to the plane of the electrode surface and the electrons in mostpart strike against the side surface of the laterals of the grid orscreen electrode and thus produce secondary electrons which uponemissionare under the influence of the electro-static field of the nextfollowing electrode of high voltage. Moreover, a large part of theelectrons hit the electrode part at glancing angles, so that for thisreason a relatively high yield of secondary electrons is produced.

By suitable choice of electrode spacing, mesh, strength of magnetic andelectric fields, a slope of the final end or tail ofthe electron orbitcan be produced directing practically the total crosssection of theelectron bundle towards one wire of the next electrode and preventingany portion of the electron bundle from passing by this electrode andstriking other electrodes which have no accelerating effect on them. Inview of the considerable curvature of the orbit of the electrons,produced by the magnetic field, it is desirable that the individualelectrodes be arranged opposite one. another in direction of thedeflection of the electrodes in order to avoid losing a part of theelectrons.

A preferred embodiment of the invention is disclosed in Fig. 1 in whichthe primary electrode l is preferably a photo-cathode. A hot cathodewith control grid can also be utilized. A plurality of grid-shapedintermediate electrodes 2, 3, 4, 5, and B are inserted between thecathode l and the anode I. These electrodes are preferably grid lateralsformed of wires perpendicular to the plane of the drawing. Allelectrodes are enclosed in a highly evacuated container 8. The magneticfield arranged according to the invention, penetrates the electrodesystem perpendicular to the plane of the drawing.

This magnetic field can be produced, for example, by the coil 9illustrated in Fig. 1. As an alternate, the container can also be placedbetween the pole pieces of a, permanent magnet or of an electro-magnet.

In Fig. 2 a portion of the discharge system is illustrated in amagnified scale. The electron orbits are indicated by dotted lines. Itis noticed that the electron travelling, for example, from grid wire 2,strikes the succeeding electrode 3 in a curved path so that when thesecondary electrons are emitted from 3 they are on the side of theelectrode 3 which is facing the electrode 4 and accordingly, areimmediately under the influence of the field produced by the highervoltage of the electrode 4.

Instead of circular grid laterals, fiat laterals can also be used. Thesefiat laterals might be strips which are bent preferably at an acuteangle towards the axis of the system and are so arranged that thesurface parts hit by the electrons face the following electrode ofhigher voltage. Such an example of this type is shown schematically inFig. 3. The axis of the system is indicated by the arrow ID. Theelectrodes consist of a number of strips which can be'formed like theso-called meshed grid in amplifier tubes. Their position to the electronorbits is apparent from the illustration in Fig. 3, namely, at an angleto the direction of the axis and also the plane of the strips formingthe same electrode are at an acute angle to the direction of the systemaxis.

Instead of arranging the individual parts of the grid or screenelectrode in planes that can be placed in curved surfaces, Fig. 4illustrates an example in which concentric electrode structure isutilized. The photo-cathode illustrated in I is preferably replaced by ahot cathode indicated by II and a control grid I2 surrounding it. Thegrid electrodes 2, 3, 4, 5, and 6 are placed radially intermediate thehot cathode ll, control grid I 2 and the anode I. The magnetic fieldprovided according to the invention is perpendicular to the plane of thedrawing and can be produced similar to the magnetic field of Fig. l. Theelectrode systems themselves are formed of Wires or strips which arearranged along a concentric cylindrical surface. Through suitable choiceof electrode space, voltage, and strength of magnetic field, theelectron orbits are substantially tangent to the electrode surfaces sothat the electrons for the most part strike surface parts and producesecondary electrons which are directed and facing the next electrode ofhigher voltage. One of such electron orbits is indicated by dotted linesin Fig. 4.

An improvement in efficiency is obtained by the grid laterals beingarranged diagonally to the magnetic field. In the use of screens withcrossed wires, the parts of the electrode diagonal to the magnetic fieldcontribute to the amplification. It is not essential that the electrodewires or laterals lie in one entirely fixed direction to the magneticfield, but it is sufficient if they lie in a surface which does not cutor only slightly cuts the magnetic field. It is also not essential forthe object of the invention that the electrons liberated at one gridlateral strike the neighboring lateral of the following electrode. It issufficient, if any lateral of this electrode is impinged u-pon. It isapparent, that many modifications may be made in the number, form andarrangement of the various parts illustrated in the preferredembodiments.

I claim:

An electron multiplier comprising a cathode and an anode spacedtherefrom, a plurality of grid electrodes therebetween, said gridelectrodes having flat laterals inclined to the axis from the cathode tothe anode and having one side facing towards the cathode and the otherside facing towards the anode, and means for curving the path ofelectrons to strike the facesof said grid electrodes facing towards theanode.

HERBERT SCI-INITGER.

